Device for limiting short-circuits



Oct. 24, 1967 H. HARTMANN 3,349,236

DEVICE FOR LIMITING SHORT-CIRCUITS Original Filed Oct. 3, 1962 2 Sheets-Sheet 1 I N VEN TOR. mm/vnprwlzvlv;

J m (1W3 1 Oct. 24, 1967 H. HARTMANN 3,349,286

DEVICE FOR LIMITING SHORT-CIRCUITS Original Filed Oct. 5, 1962 2 Sheets-Sheet 2 INVENT OR Hans Hart marm Wi -M, zufiw & ma

ATTORNEYS United States Patent 3,349,286 DEVICE FOR LIMITING SHORT-CIRCUITS Hans Hartmann, Ennetbaden, Switzerland, assignor to Brown, Boveri & Company Limited, Baden, Switzerland, a joint-stock company Continuation of application Ser. No. 228,182, Oct. 3,

1962. This application July 20, 1966, Ser. No. 566,710

5 Claims. (Cl. 31711) ABSTRACT OF THE DISCLOSURE For increasing the breaking capacity of a power switch for alternating currents particularly with respect to short circuits in the vicinity of the switch, a short circuit limiting device is connected in series with the switch. This short circuit limiting device comprises a reactance coil having an iron'core and secondary winding thereon, the core being desaturated during the Zero passage point of the alternating current, and a premagnetization transformer having a secondary winding on an iron core and interconnected with the secondary winding of the reactance coil. A primary winding common to both the reactance coil and premagnetization transformer, and which is connected in series with the switch, is constituted by a cylinder having at least one turn and surrounds the cores and secondary windings.

The invention is a continuation of application No. 228,182, now abandoned, and concerns a device for limiting short-circuits with the aid of a premagnetised reactance coil in series with the switch that has to be opened, the coil being desaturated only during the passage of the current through zero value within a cycle. For the premagnetisation, a transformer is used Which has the same primary current.

The object of this short-circuit limiting device is to increase the breaking capacity of the switch when shortcircuits occur, particularly in the vicinity of the switch. Due to the fact that the switch reactance coil is desaturated during the passage of the current through zero value, that is when the interruption occurs, the main part of the recovery voltage is on the reactance coil. This prevents the recovery voltage from causing a fiash-over at the switch contacts. This is of great importance as regards short-circuits which occur at the beginning of an overhead traction supply line in the vicinity of the switch. In this case the frequency of the recovery voltage is very high so that a very steep voltage rise occurs which increases the danger of a flash-over.

In order that the reactance coil of the switch should be desaturated at the right instant, it is necessary to premagnetise it. Without such premagnetisation, the remanence would prevent desaturation, even when the current passes through zero. When, however, the magnetisation curve is displaced by premagnetisation, it is possible to achieve the necessary desaturation just when the current passes through zero.

The premagnetisation can be obtained with additional transformers which are excited by the short-circuit current, the secondary winding of the transformers being connected to a secondary winding of the switch reactance coil. Both units are thus supplied with the same primary current.

Such switching and premagnetising reactance coils would have to be located in the switchgear plant and require a certain amount of space. They thus increase the size of the switchgear plant.

In connection with transformers which are used for current converters of the moving contact type it has already been proposed to build these transformers together 3,349,286 Patented Oct. 24, 1967 with the so-called switching reactance coils, whereby the primary winding surrounds both the core of the transformer and the reactance coil.

In order to overcome the aforementioned disadvantage, it is now proposed in accordance with the invention that the switch reactance coil and the premagnetising reactance coil should have a common primary winding which surrounds both cores, this common primary winding being in the form of a cylinder.

The inventive concept is illustrated in various embodiments in the accompanying drawings wherein:

FIG. 1 is a schematic wiring diagram for the device for limiting short circuits in association with other components of the electrical plant which cooperate therewith;

FIG. 2 is a central vertical sectional view of one embodiment of the short-circuit limiting device wherein the active components are located within an oil filled tank; and

FIGS. 3a and 311 show in longitudinal half sections alternative embodiments for another form of the short circuit limiting device wherein the active components are embedded in a casting resin, these two embodiments being symmetrical about the longitudinal axis and being illustrated respectively to the left and right of such axis.

With reference now to FIG. 1, the core of the premagnetization transformer is indicated by 1 and located on this core is the secondary winding 2. The reactance coil has a core 3 and on this core is located the secondary winding 4. The primary winding common to the premagnetization transformer and reactance coil is constituted by a cylinder type Winding of one or more turns which surrounds both cores 1 and 3 and the secondary windings 2 and 4 thereon. The total ohmic resistance of the secondary circuit represented by the interconnected secondaries 2 and 4 is indicated at 13. The terminal connecting one end of the primary winding 5 to one side of switch 11 is indicated at 9 and the other side of this switch is connected to a busbar 12. The other end of the primary winding 5 is connected to terminal 10 and from the latter to line 20. The circuit shown in FIG. 1 operates in the following manner.

After opening switch 11, the switch current ceases in its next passage through the zero point. At this moment, the secondary current has a value opposite to the instantaneous value of the switch current before its having passed through zero, thus compensating the remanence in core 3. Thereupon, the device has its maximum reactance and is ready for charging itself with the high frequency voltage returning from line 20 after switching off so that this voltage does not affect switch 11.

One suitable embodiment of the short-circuit limiting device in accordance with the invention is illustrated in FIG. 2. Here it will be seen that the cores 1 and 3 of the pre-magnetization transformer and reactance coil respectively have an annular configuration and are arranged in concentric superposed relation. The secondary windings of the transformer and reactance coil are shown at 2 and 4 respectively, and the primary winding common to both of these secondaries is seen to be comprised of inner and outer concentric cylinders or shells 5, 5 which enclose the secondaries and cores.

These active components are located within an oilfilled tank 6 provided with a cover 7. Two terminals 9 because of the large amount of current involved lead from the lower end of the inner cylinder 5' through bushings 8 to the exterior of casing 6 and are adapted to be connected to switch 11 shown in the circuit of FIG. 1. The lower end of the outer cylinder 5 is connected to terminal 10 located exteriorly of casing 6 by means of a connection sleeve 21 located interiorly of the inner cylinder 5'. Terminal is adapted to be connected to the line 20 as shown in the FIG. 1 circuit.

FIGS. 3a and 3b depict two similar embodiments of the short-circuit limiting device wherein the cores and secondary windings .of the pre-magnetization transformer and reactance coil are embedded in a casting resin. In both of these embodiments, it is the common primary winding in cylinder form which establishes the casing for the device. In the embodiment shown to the left of the center line, FIG. 3a, the annular space between the inner and outer primary cylinders 5, 5 is filled with a casting resin 14 and provided with longitudinally extending ducts 15 of an elliptical configuration depicted by 16 for circulating a cooling medium such as air, the air flow path being indicated by the arrows. The exterior of the outer primary winding cylinder 5 is .also covered with a layer of casting resin 17. This exteriorly applied casting resin 17 also establishes skirted terminal insulator sleeves 18 and 19 for the electrical terminal parts 10 and 9, respectively. The other embodiment, FIG. 3b, shown to the right of the longitudinal center line, differs from FIG. 3a only in that the outer primary winding cylinder 5 has no covering layer, and the casting resin 14 between the cylinders 5, 5 is extended exteriorly of cylinder 5 and surrounds terminal members 9 and 10 in the form of an insulating sleeve.

The advantage of this arrangement is that both reactanee coils can be located in one casing so that only one additional element is required in the switchgear plant.

I claim:

1. A short-circuit limiting device for use in reducing the adverse effect of short-circuit currents on an electrical switch connected to a line for interrupting the line, said short-circuit limiting device comprising a reactance unit and a pre-magnetizing transformer therefor, said reactance unit including a core and a secondary winding thereon and said pre-magnetizing transformer including a core and a secondary winding thereon interconnected with said secondary winding of said reactance unit, and a common primary for said reactance unit and pre-magnetizing transformer, said common primary being constituted by a cylinder having at least one turn and which surrounds said cores and secondary windings, the terminal ends of said cylinder being adapted for connection in the line in the vicinity of the switch.

2. A short-circuit limiting device as defined in claim 1 wherein said cores of said pre-magnetizing transformer and reactance unit have an annular configuration and said common primary is comprised of inner and outer concentric cylinders between which said cores and secondary windings are located.

3. A short-circuit limiting device as defined in claim 1 and whch further includes a liquid filled casing within which said pre-magnetizing transformer and reactance unit are located for insulation and cooling.

4. A short-circuit limiting device as defined in claim 1 wherein said cores and secondary windings of said premagnetizing transformer and reactance unit are embedded in a casting resin.

5. A short-circuit limiting device as defined in claim 1 wherein said cores and secondary windings of said premagnetizing transformer and reactance unit are embedded in a body of casting resin, and wherein channels are provided in said body of casting resin for passing through a fluent coolant.

References Cited UNITED STATES PATENTS 2,215,471 9/ 1940 Kesselring 31711.1 X 2,375,609 5/1945 Zuhlke 317-11.1 2,746,003 5/ 1956 Wegener 317--11.1 X 3,152,282 10/1964 Baltensperger et a1. 317-11 MILTON O. HIRSHFIELD, Primary Examiner.

R. V. LUPO, Assistant Examiner, 

1. A SHORT-CIRCUIT LIMITING DEVICE FOR USE IN REDUCING THE ADVERSE EFFECT OF SHORT-CIRCUIT CURRENTS ON AN ELECTRICAL SWITCH CONNECTED TO A LONE FOR INTERRUPTING THE LINE, SAID SHORT-CIRCUIT LIMITING DEVICE COMPRISING A REACTANCE UNIT AND A PRE-MAGNETIZING TRANSFORMER THEREFOR, SAID REACTANCE UNIT INCLUDING A CORE AND A SECONDARY WINDING THEREON AND SAID PRE-MAGNETIZING TRANSFORMER INCLUDING A CORE AND A SECONDARY WINDING THEREON INTERCONNECTED WITH SAID SECONDARY WINDING OF SAID REACTANCE UNIT, AND A COMMON PRIMARY FOR SAID REACTANCE UNIT AND PRE-MAGNETIZING TRANSFORMER, SAID COMMON PRIMARY BEING CONSTITUTED BY A CYLINDER HAVING AT LEAST ONE TURN AND WHICH SURROUNDS SAID CORES AND SECONDARY WINDINGS, THE TERMINAL ENDS OF SAID CYLINDER BEING ADAPTED FOR CONNECTION IN THE LINE IN THE VICINITY OF THE SWITCH. 